The present embodiments relate to chemical feed systems and are more particularly directed to chemical feed to a cooling tower system.
Cooling tower systems are known to remove heat, typically by circulating fluid such as water, through the system that includes the cooling tower (or more than one such tower), where the circulating water experiences a temperature drop as it passes through the tower. Cooling towers may be used in various systems where it is desired to remove heat from circulating water, or in conjunction with removing heat from another fluid by way of a heat exchanger that couples the other fluid to the circulated water of the cooling tower. For example, in an air conditioning cooling tower system, sometimes referred to as HVAC, the system includes a chiller/heat exchanger (i.e., condenser) through which the circulating cooling tower water passes and thereby removes heat from a separate chill side fluid in the chiller/heat exchanger by transferring that heat to the water that is circulating to the cooling tower. In this way, the chill side fluid may be used to cool air in the air conditioning system of buildings, hospitals, schools, businesses, and the like, while the circulating water in the cooling tower continues to circulate to carry heat away from the chiller/heat exchanger. Thus, the circulating water is cooled by the cooling tower, typically and primarily by evaporation that is achieved by ambient air crossing a flow of water, and the resulting cooled water is again circulated, again to the chiller/heat exchanger and so forth in a generally continuous loop so as to facilitate the heat transfer function.
Cooling tower systems according to the art also include apparatus to supply new water into the circulation system. Newly-added water replaces water that is lost from the circulation process, such as through evaporation of fluid by the cooling tower(s) as well as due to removal of water in order to discard solids or otherwise maintain impurities in the water at an acceptable level, where such removal is sometimes referred to as blow-down, bleed, or draw-off. Still other aspects may cause loss of water from the process, such as so-called drift (or windage), spills, and leaks. In any event, with these losses, the system includes a controlled source from which new water is introduced into the system, typically referred to as make-up water.
Cooling tower systems according to the art also include apparatus to supply chemical(s) into the circulation system so as to provide a desirable level of stability to the circulating water. The chemical may reduce or inhibit any of impurities in the water, scale, deposits, corrosion, sludge, biological activity, and any negative effect such impurities can have on the system components, such as scaling, fouling, and the like. Further, the evaporative effect provided by the cooling tower causes pure water to evaporate, thereby also causing un-evaporated residue that was in the water prior to evaporation to remain in the circulating system and, hence, over time the quantity or concentration of such residue will increase. Accordingly, it is known in the art, and the preferred embodiments are directed in this regard, to introduce chemical(s) into the cooling tower system to counterbalance, offset, and neutralize the impurities in the circulating water, thereby: (i) improving the operation of the system; (ii) significantly lengthening the amount of time that a given quantity of water may be used in the system; and (iii) reducing the necessary system maintenance that otherwise would be required from higher levels of impurities that would accumulate and the effect such impurities would have on the cooling system components.
The prior art has controlled the supply (or “feed”) of chemical(s) into a cooling tower circulation system using various approaches. While these approaches have sustained various systems, they also have certain drawbacks, as further introduced below.
In one prior art approach, a pump is electrically controlled to supply chemicals once the amount of make-up water added to the system exceeds a threshold amount. This approach relies on the assumption that make-up quantity accounts for any loss from evaporation and blow-down (and other losses). Specifically, after a certain amount of make-up water passes through a meter, the chemical pump is enabled to feed chemicals based on the amount of make-up water that meter has determined was added. This system, therefore, requires and relies upon a meter. Hence, additional costs are required from the meter. Further, if the meter is inaccurate or fails, then chemical feed is improperly controlled. Moreover, the make-up process itself may have a considerable deadband, that is, an imprecise measuring differential and corresponding time period where lost water has not yet been re-added to the system or has not been properly detected as added, such as may occur because determining the typically large volume of water in the water tower cooling systems is not trivial—this deadband, therefore, delays the addition or detection of make-up water which of course then also delays the chemical feed that only occurs after the detected make-up water volume has exceeded a threshold.
Another prior art approach is sometimes referred to as a feed and bleed system, meaning feed of chemicals is followed by a bleed, via blow-down, to obtain a proper concentration of chemicals in the system. The determination of the concentration is typically measured by a probe in the system that evaluates the conductivity of the circulating water. In response to the water conductivity, electrically-controlled apparatus such as pumps and valves are operated to feed desired amounts of chemical and to bleed water/chemicals/impurities from the system, both being adjusted until the measured conductivity is determined to be acceptable. This system therefore requires the cost of the sensor(s) and require considerable maintenance. Additionally, this system operates independently of make-up and also has a potential time lag before it reacts, so that a proper chemical balance existing before make-up may become an improper chemical balance once make-up is performed, that is, until the next iteration of the feed/bleed process following that make-up.
Given the preceding, prior art cooling tower systems and more particularly the chemical feed systems thereof have certain drawbacks. Moreover, undesirable chemical concentrations may expedite the wear on various system components, thereby decreasing operational efficiency and increasing both costs and maintenance. The preferred embodiments, therefore, seek to improve upon such considerations, as further detailed below.